How do nocturnal animals see at night?

Image Source: Erik Karits

Nocturnal animals are animals that are active at night. They sleep during the day and are active during the night.

Nocturnal animals are pretty different from diurnal(active during the day) animals in terms of senses. They have more developed senses like a better ability to see in low light and a good sense of smell and hearing.

Today, we will talk about one of their senses: sight. Nocturnal animals can see very well in presence of minimum light but what helps them to do so?

The eyes of nocturnal animals are developed in such a way that they can utilize very small amounts of light to create an image. Different morphological and anatomical adaptations that help them see at night are as follows:

BIGGER EYES

Eagle owl(left) and tarsier(right) with big eyes suited to see at night.

Image Source: Pexels

Nocturnal animals have bigger eyes as compared to diurnal creatures. Bigger eyes allow more light to fall on the eye which is essential to see anything at night.

PUPIL

The pupils of nocturnal animals dilate more. More dilation of the pupils allow more light to enter the eye.

THICK AND BIG LENS

Difference in the lens of nocturnal and diurnal animals.

Nocturnal animals have larger, thicker and more curved lenses. Due to these features, the lenses have a shorter focal length and wide aperture. The shorter focal length and wide aperture results in a low focal ratio and high light-gathering ability.

The low focal ratio results in the formation of a bright image but a smaller image.

MORE RODS THAN CONES

The retina of the eye is made up of photoreceptor(cells that respond to light) cells. The main photoreceptor cells in the retina are rods and cones. Cones help to see in bright light and register detail while rods help to see in dim light and detect motion.

This is why nocturnal animals pack more rods in their retina as compared to diurnal animals.

TAPETUM LUCIDUM

An image showing the layer of tapetum lucidum.

Image Credit: Snapshot Wisconsin

Tapetum lucidum is a retroreflective(a surface that reflects light or other forms of radiation back to its source) layer of tissue immediately behind the retina. Tapetum lucidum reflects the light unabsorbed by the retina on the initial transmission of the light. This gives the retina a second chance to absorb the light.

Eyeshine in raccoon.

Image Source: Wikimedia

If the light is not absorbed by the retina on the second chance also, it leaves the eye through the pupil and results in eyeshine(glowing of an animal's eye in the dark).